Line Buffer Unit for Image Processor

ABSTRACT

An apparatus is described that include a line buffer unit composed of a plurality of a line buffer interface units. Each line buffer interface unit is to handle one or more requests by a respective producer to store a respective line group in a memory and handle one or more requests by a respective consumer to fetch and provide the respective line group from memory. The line buffer unit has programmable storage space whose information establishes line group size so that different line group sizes for different image sizes are storable in memory.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 16/402,310, filed on May 3, 2019, which is acontinuation of and claims priority to U.S. patent application Ser. No.15/598,027, filed on May 17, 2017, which is a continuation of and claimspriority to U.S. patent application Ser. No. 14/694,712, filed on Apr.23, 2015, the entire contents of each are hereby incorporated byreference.

FIELD OF INVENTION

The field of invention pertains generally to image processing, and, morespecifically, to a line buffer unit for an image processor.

BACKGROUND

Image processing typically involves the processing of pixel values thatare organized into an array. Here, a spatially organized two dimensionalarray captures the two dimensional nature of images (additionaldimensions may include time (e.g., a sequence of two dimensional images)and data type (e.g., colors). In a typical scenario, the arrayed pixelvalues are provided by a camera that has generated a still image or asequence of frames to capture images of motion. Traditional imageprocessors typically fall on either side of two extremes.

A first extreme performs image processing tasks as software programsexecuting on a general purpose processor or general purpose-likeprocessor (e.g., a general purpose processor with vector instructionenhancements). Although the first extreme typically provides a highlyversatile application software development platform, its use of finergrained data structures combined with the associated overhead (e.g.,instruction fetch and decode, handling of on-chip and off-chip data,speculative execution) ultimately results in larger amounts of energybeing consumed per unit of data during execution of the program code.

A second, opposite extreme applies fixed function hardwired circuitry tomuch larger blocks of data. The use of larger (as opposed to finergrained) blocks of data applied directly to custom designed circuitsgreatly reduces power consumption per unit of data. However, the use ofcustom designed fixed function circuitry generally results in a limitedset of tasks that the processor is able to perform. As such, the widelyversatile programming environment (that is associated with the firstextreme) is lacking in the second extreme.

A technology platform that provides for both highly versatileapplication software development opportunities combined with improvedpower efficiency per unit of data remains a desirable yet missingsolution.

SUMMARY

An apparatus is described that include a line buffer unit composed of aplurality of a line buffer interface units. Each line buffer interfaceunit is to handle one or more requests by a respective producer to storea respective line group in a memory and handle one or more requests by arespective consumer to fetch and provide the respective line group frommemory. The line buffer unit has programmable storage space whoseinformation establishes line group size so that different line groupsizes for different image sizes are storable in memory.

LIST OF FIGURES

The following description and accompanying drawings are used toillustrate embodiments of the invention. In the drawings:

FIG. 1 shows various components of a technology platform;

FIG. 2a shows an embodiment of application software built with kernels;

FIG. 2b shows an embodiment of the structure of a kernel;

FIG. 3 shows an embodiment of the operation of a kernel;

FIG. 4 shows an embodiment of an image processor hardware architecture;

FIGS. 5a, 5b, 5c, 5d and 5e depict the parsing of image data into a linegroup, the parsing of a line group into a sheet and the operationperformed on a sheet with overlapping stencils;

FIG. 6 shows an embodiment of a stencil processor;

FIG. 7 shows an embodiment of the configuration and programming of animage processor

FIG. 8 shows an image frame composed of line groups;

FIGS. 9a, 9b and 9c depict design and operational embodiments of a linebuffer unit;

FIGS. 9d and 9e depict embodiments of programmable register space of animage processor;

FIGS. 10a and 10b depict a virtually tall mode of operation;

FIGS. 11a and 11b show line buffer interface unit embodiments;

FIG. 12 shows an embodiment of a computing system.

DETAILED DESCRIPTION i. Introduction

The description below describes numerous embodiments concerning a newimage processing technology platform that provides a widely versatileapplication software development environment that uses larger blocks ofdata (e.g., line groups and sheets as described further below) toprovide for improved power efficiency.

1.0 Application Software Development Environment

a. Application and Structure of Kernels

FIG. 1 shows a high level view of an image processor technology platformthat includes a virtual image processing environment 101, the actualimage processing hardware 103 and a compiler 102 for translating higherlevel code written for the virtual processing environment 101 to objectcode that the actual hardware 103 physically executes. As described inmore detail below, the virtual processing environment 101 is widelyversatile in terms of the applications that can be developed and istailored for easy visualization of an application's constituentprocesses. Upon completion of the program code development effort by thedeveloper 104, the compiler 102 translates the code that was writtenwithin the virtual processing environment 101 into object code that istargeted for the actual hardware 103.

FIG. 2a shows an example of the structure and form that applicationsoftware written within the virtual environment may take. As observed inFIG. 2a , the program code may be expected to process one or more framesof input image data 201 to effect some overall transformation on theinput image data 201. The transformation is realized with the operationof one or more kernels of program code 202 that operate on the inputimage data in an orchestrated sequence articulated by the developer.

For example, as observed in FIG. 2a , the overall transformation iseffected by first processing each input image with a first kernel K1.The output images produced by kernel K1 are then operated on by kernelK2. Each of the output images produced by kernel K2 are then operated onby kernel K3_1 or K3_2, The output images produced by kernel(s)K3_1/K3_2 are then operated on by kernel K4. Kernels K3_1 and K3_2 maybe identical kernels designed to speed-up the overall processing byimposing parallel processing at the K3 stage, or, may be differentkernels (e.g., kernel K3_1 operates on input images of a first specifictype and kernel K3_2 operates on input images of a second, differenttype).

As such, the larger overall image processing sequence may take the formof a image processing pipeline or a directed acyclic graph (DAG) and thedevelopment environment may be equipped to actually present thedeveloper with a representation of the program code being developed assuch. Kernels may be developed by a developer individually and/or may beprovided by an entity that supplies any underlying technology (such asthe actual signal processor hardware and/or a design thereof) and/or bya third party (e.g., a vendor of kernel software written for thedevelopment environment). As such, it is expected that a nominaldevelopment environment will include a “library” of kernels thatdevelopers are free to “hook-up” in various ways to effect the overallflow of their larger development effort. Some basic kernels that areexpected to be part of such a library may include kernels to provide anyone or more of the following basic image processing tasks: convolutions,denoising, color space conversions, edge and corner detection,sharpening, white balance, gamma correction, tone mapping, matrixmultiply, image registration, pyramid construction, wavelettransformation, block-wise discrete cosine and Fourier transformations.

FIG. 2b shows an exemplary depiction of the structure of a kernel 203 asmay be envisioned by a developer. As observed in FIG. 2b , the kernel203 can be viewed as a number of parallel threads of program code(“threads”) 204 that are each operating on a respective underlyingprocessor 205 where each processor 205 is directed to a particularlocation in an output array 206 (such as a specific pixel location inthe output image that the kernel is generating). For simplicity onlythree processors and corresponding threads are shown in FIG. 2b . Invarious embodiments, every depicted output array location would have itsown dedicated processor and corresponding thread. That is, a separateprocessor and thread can be allocated for each pixel in the outputarray.

As will be described in more detail below, in various embodiments, inthe actual underlying hardware an array of execution lanes andcorresponding threads operate in unison (e.g., in a Single InstructionMultiple Data (s) like fashion) to generate output image data for aportion of a “line group” of the frame currently being processed. A linegroup is a contiguous, sizable section of an image frame. In variousembodiments, the developer may be conscious the hardware operates online groups, or, the development environment may present an abstractionin which there is a separate processor and thread for, e.g., every pixelin the output frame (e.g., every pixel in an output frame generated byits own dedicated processor and thread). Regardless, in variousembodiment, the developer understands the kernel to include anindividual thread for each output pixel (whether the output array isvisualized is an entire output frame or a section thereof).

As will be described in more detail below, in an embodiment theprocessors 205 that are presented to the developer in the virtualenvironment have an instruction set architecture (ISA) that, not onlysupports standard (e.g., RISC) opcodes, but also include speciallyformatted data access instructions that permit the developer to easilyvisualize the pixel by pixel processing that is being performed. Theability to easily define/visualize any input array location incombination with an entire ISA of traditional mathematical and programcontrol opcodes allows for an extremely versatile programmingenvironment that essentially permits an application program developer todefine, ideally, any desired function to be performed on any sized imagesurface. For example, ideally, any mathematical operation can be readilyprogrammed to be applied to any stencil size.

With respect to the data access instructions, in an embodiment the ISAof the virtual processors (“virtual ISA”) include a special data loadinstruction and a special data store instruction. The data loadinstruction is able to read from any location within an input array ofimage data. The data store instruction is able to write to any locationwithin the output array of image data. The latter instruction allows foreasily dedicating multiple instances of the same processor to differentoutput pixel locations (each processor writes to a different pixel inthe output array). As such, for example, stencil size itself (e.g.,expressed as a width of pixels and a height of pixels) can be made aneasily programmable feature. Visualization of the processing operationsis further simplified with each of the special load and storeinstructions having a special instruction format whereby target arraylocations are specified simplistically as X and Y coordinates.

Regardless, by instantiating a separate processor for each of multipleslocations in the output array, the processors can execute theirrespective threads in parallel so that, e.g., the respective values forall locations in the output array are produced concurrently. It isnoteworthy that many image processing routines typically perform thesame operations on different pixels of the same output image. As such,in one embodiment of the development environment, each processor ispresumed to be identical and executes the same thread program code.Thus, the virtualized environment can be viewed as a type oftwo-dimensional (2D), SIMD processor composed of a 2D array of, e.g.,identical processors each executing identical code in lock-step.

FIG. 3 shows a more detailed example of the processing environment fortwo virtual processors that are processing identical code for twodifferent pixel locations in an output array. FIG. 3 shows an outputarray 304 that corresponds to an output image being generated. Here, afirst virtual processor is processing the code of thread 301 to generatean output value at location X1 of the output array 304 and a secondvirtual processor is processing the code of thread 302 to generate anoutput value at location X2 of the output array 304. Again, in variousembodiments, the developer would understand there is a separateprocessor and thread for each pixel location in the output array 304(for simplicity FIG. 3 only shows two of them). However, the developerin various embodiments need only develop code for one processor andthread (because of the SIMD like nature of the machine).

As is known in the art, an output pixel value is often determined byprocessing the pixels of an input array that include and surround thecorresponding output pixel location. For example, as can be seen fromFIG. 3, position X1 of the output array 304 corresponds to position E ofthe input array 303. The stencil of input array 303 pixel values thatwould be processed to determine output value X1 would thereforecorresponds to input values ABCDEFGHI. Similarly, the stencil of inputarray pixels that would be processed to determine output value X2 wouldcorresponds to input values DEFGHIJKL.

FIG. 3 shows an example of corresponding virtual environment programcode for a pair of threads 301, 302 that could be used to calculateoutput values X1 and X2, respectively. In the example of FIG. 3 bothpairs of code are identical and average a stencil of nine input arrayvalues to determine a corresponding output value. The only differencebetween the two threads is the variables that are called up from theinput array and the location of the output array that is written to.Specifically, the thread that writes to output location X1 operates onstencil ABCDEFGHI and the thread that writes to output location X2operates on stencil DEFGHIJKL.

As can be seen from the respective program code from the pair of threads301, 302, each virtual processor at least includes internal registers R1and R2 and at least supports the following instructions: 1) a LOADinstruction from the input array into R1; 2) a LOAD instruction from theinput array into R2; 3) an ADD instruction that adds the contents of R1and R2 and places the resultant in R2; 4) a DIV instruction that dividesthe value within R2 by immediate operand 9; and, 5) a STORE instructionthe stores the contents of R2 into the output array location that thethread is dedicated to. Again, although only two output array locationsand only two threads and corresponding processors are depicted in FIG.3, conceivably, every location in the output array could be assigned avirtual processor and corresponding thread that performs thesefunctions. In various embodiments, in keeping with the SIMD-like natureof the processing environment, the multiple threads execute in isolationof one another. That is, there is no thread-to-thread communicationbetween virtual processors (one SIMD channel is preventing from crossinginto another SIMD channel).

b. Virtual Processor Memory Model

In various embodiments, a pertinent feature of the virtual processors istheir memory model. As is understood in the art, a processor reads datafrom memory, operates on that data and writes new data back into memory.A memory model is the perspective or view that a processor has of themanner in which data is organized in memory. In an embodiment, thememory model of the virtual processors includes both input and outputarray regions. Input pixel values for threads are stored in the inputarray region and output pixel values generated by threads are stored inthe output array region.

In an embodiment, a novel memory addressing scheme is used to definewhich particular input values are to be called in from an input arrayportion of the virtual processor's memory model. Specifically, a“position relative” addressing scheme is used that defines the desiredinput data with X, Y coordinates rather than a traditional linear memoryaddress. As such, the load instruction of the virtual processors' ISAincludes an instruction format that identifies a specific memorylocation within the input array with an X component and a Y component.As such, a two-dimensional coordinate system is used to address memoryfor input values read from the input array.

The use of a position relative memory addressing approach permits theregion of an image that a virtual processor is operating on to be morereadily identifiable to a developer. As mentioned above, the ability toeasily define/visualize any input array location in combination with anentire ISA of traditional mathematical and program control opcodesallows for an extremely versatile programming environment thatessentially permits an application program developer to readily define,ideally, any desired function to be performed on any sized imagesurface. Various instruction format embodiments for instructions thatadopt a position relative addressing scheme, as well as embodiments ofother features of the supported ISA, are described in more detailfurther below.

The output array contains the output image data that the threads areresponsible for generating. The output image data may be final imagedata such as the actual image data that is presented on a display thatfollows the overall image processing sequence, or, may be intermediateimage data that a subsequent kernel of the overall image processingsequence uses as its input image data information. Again, typicallyvirtual processors do not compete for same output data items becausethey write to different pixel locations of the output image data duringa same cycle.

In an embodiment, the position relative addressing scheme is also usedfor writes to the output array. As such, the ISA for each virtualprocessor includes a store instruction whose instruction format definesa targeted write location in memory as a two-dimensional X, Y coordinaterather than a traditional random access memory address.

2.0 Hardware Architecture Embodiments

a. Image Processor Hardware Architecture and Operation

FIG. 4 shows an embodiment of an architecture 400 for an image processorimplemented in hardware. The image processor may be targeted, forexample, by a compiler that converts program code written for a virtualprocessor within a simulated environment into program code that isactually executed by the hardware processor. As observed in FIG. 4, thearchitecture 400 includes a plurality of line buffer units 401_1 through401_M interconnected to a plurality of stencil processor units 402_1through 402_N and corresponding sheet generator units 403_1 through403_N through a network 404 (e.g., a network on chip (NOC) including anon chip switch network, an on chip ring network or other kind ofnetwork). In an embodiment, any line buffer unit may connect to anysheet generator and corresponding stencil processor through the network404.

In an embodiment, program code is compiled and loaded onto acorresponding stencil processor 402 to perform the image processingoperations earlier defined by a software developer (program code mayalso be loaded onto the stencil processor's associated sheet generator403, e.g., depending on design and implementation). In at least someinstances an image processing pipeline may be realized by loading afirst kernel program for a first pipeline stage into a first stencilprocessor 402_1, loading a second kernel program for a second pipelinestage into a second stencil processor 402_2, etc. where the first kernelperforms the functions of the first stage of the pipeline, the secondkernel performs the functions of the second stage of the pipeline, etc.and additional control flow methods are installed to pass output imagedata from one stage of the pipeline to the next stage of the pipeline.

In other configurations, the image processor may be realized as aparallel machine having two or more stencil processors 402_1, 402_2operating the same kernel program code. For example, a highly dense andhigh data rate stream of image data may be processed by spreading framesacross multiple stencil processors each of which perform the samefunction.

In yet other configurations, essentially any DAG of kernels may beloaded onto the hardware processor by configuring respective stencilprocessors with their own respective kernel of program code andconfiguring appropriate control flow hooks into the hardware to directoutput images from one kernel to the input of a next kernel in the DAGdesign.

As a general flow, frames of image data are received by a macro I/O unit405 and passed to one or more of the line buffer units 401 on a frame byframe basis. A particular line buffer unit parses its frame of imagedata into a smaller region of image data, referred to as a “a linegroup”, and then passes the line group through the network 404 to aparticular sheet generator. A complete or “full” singular line group maybe composed, for example, with the data of multiple contiguous completerows or columns of a frame (for simplicity the present specificationwill mainly refer to contiguous rows). The sheet generator furtherparses the line group of image data into a smaller region of image data,referred to as a “sheet”, and presents the sheet to its correspondingstencil processor.

In the case of an image processing pipeline or a DAG flow having asingle input, generally, input frames are directed to the same linebuffer unit 401_1 which parses the image data into line groups anddirects the line groups to the sheet generator 403_1 whose correspondingstencil processor 402_1 is executing the code of the first kernel in thepipeline/DAG. Upon completion of operations by the stencil processor402_1 on the line groups it processes, the sheet generator 403_1 sendsoutput line groups to a “downstream” line buffer unit 401_2 (in some usecases the output line group may be sent_back to the same line bufferunit 401_1 that earlier had sent the input line groups).

One or more “consumer” kernels that represent the next stage/operationin the pipeline/DAG executing on their own respective other sheetgenerator and stencil processor (e.g., sheet generator 403_2 and stencilprocessor 402_2) then receive from the downstream line buffer unit 401_2the image data generated by the first stencil processor 402_1. In thismanner, a “producer” kernel operating on a first stencil processor hasits output data forwarded to a “consumer” kernel operating on a secondstencil processor where the consumer kernel performs the next set oftasks after the producer kernel consistent with the design of theoverall pipeline or DAG.

A stencil processor 402 is designed to simultaneously operate onmultiple overlapping stencils of image data. The multiple overlappingstencils and internal hardware processing capacity of the stencilprocessor effectively determines the size of a sheet. Here, within astencil processor 402, arrays of execution lanes operate in unison tosimultaneously process the image data surface area covered by themultiple overlapping stencils.

As will be described in more detail below, in various embodiments,sheets of image data are loaded into a two-dimensional register arraystructure within the stencil processor 402. The use of sheets and thetwo-dimensional register array structure is believed to effectivelyprovide for power consumption improvements by moving a large amount ofdata into a large amount of register space as, e.g., a single loadoperation with processing tasks performed directly on the dataimmediately thereafter by an execution lane array. Additionally, the useof an execution lane array and corresponding register array provide fordifferent stencil sizes that are easily programmable/configurable.

FIGS. 5a through 5e illustrate at a high level embodiments of both theparsing activity of a line buffer unit 401, the finer grained parsingactivity of a sheet generator unit 403 as well as the stencil processingactivity of the stencil processor 402 that is coupled to the sheetgenerator unit 403.

FIG. 5a depicts an embodiment of an input frame of image data 501. FIG.5a also depicts an outline of three overlapping stencils 502 (eachhaving a dimension of 3 pixels×3 pixels) that a stencil processor isdesigned to operate over. The output pixel that each stencilrespectively generates output image data for is highlighted in solidblack. For simplicity, the three overlapping stencils 502 are depictedas overlapping only in the vertical direction. It is pertinent torecognize that in actuality a stencil processor may be designed to haveoverlapping stencils in both the vertical and horizontal directions.

Because of the vertical overlapping stencils 502 within the stencilprocessor, as observed in FIG. 5a , there exists a wide band of imagedata within the frame that a single stencil processor can operate over.As will be discussed in more detail below, in an embodiment, the stencilprocessors process data within their overlapping stencils in a left toright fashion across the image data (and then repeat for the next set oflines, in top to bottom order). Thus, as the stencil processors continueforward with their operation, the number of solid black output pixelblocks will grow right-wise horizontally. As discussed above, a linebuffer unit 401 is responsible for parsing a line group of input imagedata from an incoming frame that is sufficient for the stencilprocessors to operate over for an extended number of upcoming cycles. Anexemplary depiction of a line group is illustrated as a shaded region503. In an embodiment, as described further below, the line buffer unit401 can comprehend different dynamics for sending/receiving a line groupto/from a sheet generator. For example, according to one mode, referredto as “full group”, the complete full width lines of image data arepassed between a line buffer unit and a sheet generator. According to asecond mode, referred to as “virtually tall”, a line group is passedinitially with a subset of full width rows. The remaining rows are thenpassed sequentially in smaller (less than full width) pieces.

With the line group 503 of the input image data having been defined bythe line buffer unit and passed to the sheet generator unit, the sheetgenerator unit further parses the line group into finer sheets that aremore precisely fitted to the hardware limitations of the stencilprocessor. More specifically, as will be described in more detailfurther below, in an embodiment, each stencil processor consists of atwo dimensional shift register array. The two dimensional shift registerarray essentially shifts image data “beneath” an array of executionlanes where the pattern of the shifting causes each execution lane tooperate on data within its own respective stencil (that is, eachexecution lane processes on its own stencil of information to generatean output for that stencil). In an embodiment, sheets are surface areasof input image data that “fill” or are otherwise loaded into the twodimensional shift register array.

Thus, as observed in FIG. 5b , the sheet generator parses an initialsheet 504 from the line group 503 and provides it to the stencilprocessor (here, the sheet of data corresponds to the shaded region thatis generally identified by reference number 504). As observed in FIGS.5c and 5d , the stencil processor operates on the sheet of input imagedata by effectively moving the overlapping stencils 502 in a left toright fashion over the sheet. As of FIG. 5d , the number of pixels forwhich an output value could be calculated from the data within the sheetis exhausted (no other pixel positions can have an output valuedetermined from the information within the sheet). For simplicity theborder regions of the image have been ignored.

As observed in FIG. 5e the sheet generator then provides a next sheet505 for the stencil processor to continue operations on. Note that theinitial positions of the stencils as they begin operation on the nextsheet is the next progression to the right from the point of exhaustionon the first sheet (as depicted previously in FIG. 5d ). With the newsheet 505, the stencils will simply continue moving to the right as thestencil processor operates on the new sheet in the same manner as withthe processing of the first sheet.

Note that there is some overlap between the data of the first sheet 504and the data of the second sheet 505 owing to the border regions ofstencils that surround an output pixel location. The overlap could behandled simply by the sheet generator re-transmitting the overlappingdata twice. In alternate implementations, to feed a next sheet to thestencil processor, the sheet generator may proceed to only send new datato the stencil processor and the stencil processor reuses theoverlapping data from the previous sheet.

b. Stencil Processor Design and Operation

FIG. 6 shows an embodiment of a stencil processor architecture 600. Asobserved in FIG. 6, the stencil processor includes a data computationunit 601, a scalar processor 602 and associated memory 603 and an I/Ounit 604. The data computation unit 601 includes an array of executionlanes 605, a two-dimensional shift array structure 606 and separaterandom access memories 607 associated with specific rows or columns ofthe array.

The I/O unit 604 is responsible for loading “input” sheets of datareceived from the sheet generator into the data computation unit 601 andstoring “output” sheets of data from the stencil processor into thesheet generator. In an embodiment the loading of sheet data into thedata computation unit 601 entails parsing a received sheet intorows/columns of image data and loading the rows/columns of image datainto the two dimensional shift register structure 606 or respectiverandom access memories 607 of the rows/columns of the execution lanearray (described in more detail below). If the sheet is initially loadedinto memories 607, the individual execution lanes within the executionlane array 605 may then load sheet data into the two-dimensional shiftregister structure 606 from the random access memories 607 whenappropriate (e.g., as a load instruction just prior to operation on thesheet's data). Upon completion of the loading of a sheet of data intothe register structure 606 (whether directly from a sheet generator orfrom memories 607), the execution lanes of the execution lane array 605operate on the data and eventually “write back” finished data as a sheetdirectly back to the sheet generator, or, into the random accessmemories 607. If the later the I/O unit 604 fetches the data from therandom access memories 607 to form an output sheet which is thenforwarded to the sheet generator.

The scalar processor 602 includes a program controller 609 that readsthe instructions of the stencil processor's program code from scalarmemory 603 and issues the instructions to the execution lanes in theexecution lane array 605. In an embodiment, a single same instruction isbroadcast to all execution lanes within the array 605 to effect aSIMD-like behavior from the data computation unit 601. In an embodiment,the instruction format of the instructions read from scalar memory 603and issued to the execution lanes of the execution lane array 605includes a very-long-instruction-word (VLIW) type format that includesmore than one opcode per instruction. In a further embodiment, the VLIWformat includes both an ALU opcode that directs a mathematical functionperformed by each execution lane's ALU (which, as described below, in anembodiment may specify more than one traditional ALU operation) and amemory opcode (that directs a memory operation for a specific executionlane or set of execution lanes).

The term “execution lane” refers to a set of one or more execution unitscapable of executing an instruction (e.g., logic circuitry that canexecute an instruction). An execution lane can, in various embodiments,include more processor-like functionality beyond just execution units,however. For example, besides one or more execution units, an executionlane may also include logic circuitry that decodes a receivedinstruction, or, in the case of more MIMD-like designs, logic circuitrythat fetches and decodes an instruction. With respect to MIMD-likeapproaches, although a centralized program control approach has largelybeen described herein, a more distributed approach may be implemented invarious alternative embodiments (e.g., including program code and aprogram controller within each execution lane of the array 605).

The combination of an execution lane array 605, program controller 609and two dimensional shift register structure 606 provides a widelyadaptable/configurable hardware platform for a broad range ofprogrammable functions. For example, application software developers areable to program kernels having a wide range of different functionalcapability as well as dimension (e.g., stencil size) given that theindividual execution lanes are able to perform a wide variety offunctions and are able to readily access input image data proximate toany output array location.

Apart from acting as a data store for image data being operated on bythe execution lane array 605, the random access memories 607 may alsokeep one or more look-up tables. In various embodiments one or morescalar look-up tables may also be instantiated within the scalar memory603.

A scalar look-up involves passing the same data value from the samelook-up table from the same index to each of the execution lanes withinthe execution lane array 605. In various embodiments, the VLIWinstruction format described above is expanded to also include a scalaropcode that directs a look-up operation performed by the scalarprocessor into a scalar look-up table. The index that is specified foruse with the opcode may be an immediate operand or fetched from someother data storage location. Regardless, in an embodiment, a look-upfrom a scalar look-up table within scalar memory essentially involvesbroadcasting the same data value to all execution lanes within theexecution lane array 605 during the same clock cycle.

3.0 Line Buffer Unit Embodiments

a. Line Buffer Unit Overview

Recall from the discussion above in Section 1.0 that in variousembodiments, program code that is written for the hardware platform iswritten with a unique virtual code that includes an instruction sethaving load and store instructions whose instruction format identifiesinput and output array locations as, e.g., X,Y coordinates. In variousimplementations, the X,Y coordinate information may actually beprogrammed into the hardware platform and recognized/understood byvarious ones of its components. This stands apart from, for example,translating the X,Y coordination (e.g., within the compiler) intodifferent information. For example, in the case of the two-dimensionalshift register structure within the stencil processor, the X,Ycoordinate information is translated into register shift movements. Bycontrast, other parts of the hardware platform may specifically receiveand comprehend the X,Y coordinate information originally expressed atthe higher, virtual code level.

As observed in FIG. 7, as described in Section 1.0, a program codedeveloper expresses data locations as X,Y coordinates with the specialinstruction format at the virtual code level 710. During the compilationstage, the virtual code is translated into program code that is actuallyprocessed by the hardware (object code) and corresponding configurationinformation that is loaded into the hardware's configuration (e.g.,register) space. As observed in FIG. 7, in an embodiment, the objectcode for a particular kernel is loaded into the program space of thestencil processor's scalar processor 705.

As part of the configuration process, configuration software executingon the scalar processor 705 loads the appropriate configurationinformation 711, 712 into both the sheet generator unit 703 that iscoupled to the stencil processor 702, and, the line buffer unit 701 thatwill generate new sheets for the stencil processor 702 to operate on,or, receive processed sheets generated by the stencil processor 702.Here, generally, sheets can still be contemplated in terms of X,Ycoordinates of an overall image. That is, once an image or frame isdefined (e.g., in terms of number of pixels per row, number of rows,number of pixels per column and number of columns), any portion orposition of the image can still be referred to with X,Y coordinates.

As such, in various embodiments, either or both of the sheet generatorunit 703 and line buffer unit 701 are configured with information 711,712 within their respective configuration space 706, 707 thatestablishes an informational platform from which specific locationsand/or regions (e.g., line groups, sheets) of an image or frame areidentified in X,Y coordinates. In various implementations/uses, the X,Ycoordinates may be the same X,Y coordinates expressed at the virtualcode level.

Examples of such information include, e.g., number of active line groupsin the line buffer unit, image size for each line group (e.g., as a setof four X, Y coordinates (one for each corner) or a pair of X, Ycoordinates (one for a lower nearer corner and one for an upper farthercorner)), absolute image width and image height, stencil size (expressedas X, Y values that define the size of a single stencil and/or the areaof the overlapping stencils of the stencil processor), sheet and/or linegroup size (e.g., specified in same terms as an image size but havingsmaller dimensions), etc. Additionally, the line buffer unit 701 atleast may be programmed with additional configuration information suchas the number of producer kernels writing and the number of consumerkernels reading the line groups that are managed by the line buffer unit701. The number of channels and/or the dimensions associated with theimage data are also typically included as configuration information.

FIG. 8 depicts the use of X,Y coordinates to define, as just oneexample, line groups within an image. Here, N line groups 801_1, 801_2,. . . 801_N are observable within an image 801. As can be seen from FIG.8, each line group can be readily defined by reference to X, Ycoordinates within the image that define, e.g., one or more of a linegroup's corner points. As such, in various embodiments, a line group'sname or other data structure used to define a particular line group mayinclude X, Y coordinate locations associated with the line group inorder to particularly identify it.

Referring briefly back to FIG. 7, note that FIG. 7 shows that duringruntime, a sheet generator 703 may request a “next” line group (orportion of a line group) from the line buffer unit 701 by, e.g.,including X, Y coordinate information that defines the desired dataregion. FIG. 8 shows nominal “full width” line groups composed only ofcomplete rows of image data. In an alternative configuration referred toas “virtually-tall”, described in more detail further below, the linebuffer unit 701 initially passes only a first upper portion of a linegroup as full width rows of image data. The subsequent lower rows of theline group are then specifically requested for by the sheet generator incontiguous chunks that are less than a full width row and are separatelyrequested for. As such, multiple requests are made by the sheetgenerator in order to obtain the full line group. Here, each suchrequest may define a next lower portion by X, Y coordinates that areattributable to the next lower portion.

FIGS. 9a through 9c demonstrate various features of a line buffer unitembodiment 900. As observed in FIG. 9a , a line buffer unit includesmemory 902 in which line groups 903_1 through 903_N are stored (e.g.,static or dynamic random access memory (SRAM or DRAM)). FIG. 9a showsthe activity between the various kernels that produce and consume theline groups 903_1 through 903_N for a particular image/frame within thememory 902.

As observed in FIG. 9a , a producer kernel K1 sends new line groups tothe memory 902 over separate time instances P1, P2 through PN. Theproducer kernel K1 executes on a stencil processor that generates newsheets of data. The sheet generator that is coupled to the stencilprocessor accumulates sheets to form line groups and forwards the linegroups to the memory 902.

Also as depicted in FIG. 9a , there are two consumer kernels K2, K3 thatoperate on the line groups 903_1 through 903_N generated by producerkernel K1. Here, consumer kernels K2 and K3 receive the first line group903_1 at times C21 and C31, respectively. Obviously, times C21 and C31occur after time P1. Other restrictions may not exist. For example timesC21 and/or C31 may occur before or after any of times P2 through PN.Here, the respective sheet generators for kernels K2 and K3 request anext line group at a time that is appropriate for their respectivekernel. If any of kernels K2, K3 request line group 903_1 before timeP1, the request idles until after line group 903_1 is actually writteninto memory 902. In many implementations, a producer kernel operates ona different stencil processor than a consumer kernel.

Conceivably, requests from either or both of kernels K2 and K3 for allof line groups 903_1 through 903_N may arrive prior to time P1. Thus,line groups may be requested by consumer kernels at any time. The linegroups are forwarded to the consumer kernels as they request themsubject, however, to the rate at which the producer kernel K1 canproduce them. In various embodiments, consumer kernels request linegroups in sequence and likewise receive them in sequence (kernel K2receives line groups 902_2 through 902_N at times C22 through C2N insequence). For simplicity only one producer kernel is depicted for aparticular line group. It is conceivable that various embodiments may bedesigned to permit different producers to write to a same line group(e.g., where consumers are not permitted to be serviced until after allproducers have written to the line group).

In cases where there is no producer kernel (because the consumerkernel(s) is/are the first kernels in the processor's DAG processingflow), frames of image data may be transferred into memory 902 (e.g.,via direct memory access (DMA) or from a camera) and parsed into linegroups. In cases where there are no consumer kernel(s) (because theproducer kernel is the last kernel in the processor's overall programflow), resultant line groups may be combined to form output frames.

FIG. 9b shows a more detailed embodiment of an entire line buffer unit900. For the sake of discussion, the activity of FIG. 9a is superimposedon the line buffer unit 900 of FIG. 9b . As can be seen in FIG. 9b , aline buffer unit 900 includes memory 902 coupled to line buffer unitcircuitry 901. Line buffer unit circuitry 901 may be constructed, forexample, with dedicated logic circuitry. Within line buffer unitcircuitry 901, a line buffer interface unit 904_1 through 904_N isreserved for each line group 903_1 through 903_N within memory 902. Invarious embodiments, there is a fixed number of line buffer interfaceunits 904_1 through 904_N which sets an upper limit on the number ofline groups that a line buffer unit can manage at any instant of time(if fewer than N line groups are active, a corresponding smaller numberof line buffer unit interfaces are activated and in use at any time).

As depicted in FIG. 9b , with a total number of N line buffer interfaceunits 904 within the line buffer unit circuitry 901, the line bufferunit 900 is handling a maximum number of line groups. Additionally, witha largest permitted line group size (where line group size is aconfigurable parameter) an approximate size for memory 902 can bedetermined (of course, to allow for hardware efficiencies a smallermemory footprint may be instantiated at the cost of not simultaneouslypermitting N maximum sized line groups).

Each line buffer interface unit 904_1 through 904_N is responsible forhandling the producer and consumer requests for a particular line groupthat it has been assigned to handle. For example, line buffer interfaceunit 904_1 handles the request from producer K1 at time P1 to store linegroup 903_1 as well as handles the requests from consumer kernels K2 andK3 for line group 903_1. In response to the former, line bufferinterface unit 904_1 writes line group 903_1 into memory 902. Inresponse to the latter, line buffer interface unit 904_1 performsrespective reads of line group 903_1 from memory 902 and forwards linegroup 903_1 to consumers K2 and K3 at times C21 and C31, respectively.

After all consumers of a line group have been forwarded their copy ofthe line group, the line buffer interface unit is “free” to be assignedto another line group. For example, if line group 903_1 represents thefirst line group within a first image frame of a sequence of frames,after line group 903_1 has been forwarded to consumers K2 and K3 attimes C21 and C31, line buffer interface unit 904_1 may next be assignedto handle the first line group within the next, second image frame ofthe sequence of frames. In this manner, the line buffer unit circuitry901 can be viewed as having a “pool” of line buffer interface units 904where each interface unit is assigned a new line group to manage afterits immediately preceding line group was delivered to its last consumer.Thus, there is a rotation of interface units as they repeatedly enterand are removed from a “free pool” of line buffer interface units whohave served their last consumer and are waiting for their next linegroup.

FIG. 9c illustrates an embodiment of the rotation in more detail. Asobserved in FIG. 9c , an available line buffer interface unit isselected from a free pool of line buffer interface units within the linebuffer unit circuitry 910. The line buffer interface unit is thenconfigured with appropriate configuration information 911 (e.g., X, Yposition information of the new line group or a linear memory addressequivalent). Here, note in FIG. 9b that each line buffer interface unitmay include configuration register space 905 where such configurationinformation is kept.

The line buffer interface unit then proceeds to handle producer andconsumer requests for its newly assigned line group 912. After the lastproducer has written to the line group (in various embodiments there isonly one producer per line group) and after the last consumer has beenprovided with the version of the line group that has been written to byits producer(s), the line buffer interface unit is returned to the freepool and the process repeats 910 for a next line group. The controllogic circuitry within the line buffer unit circuitry 901 that overseesthe control flow of FIG. 9c is not depicted in FIG. 9b for illustrativeconvenience.

b. Programmable Register Space Embodiments

With respect to the updated configuration information 911 that isprovided to a line buffer interface unit as part of the assignment of anext line group, in a nominal case, the line buffer unit 900 itself ishandling a static arrangement of, e.g., only one fixed producer that isfeeding a fixed set of one or more consumers. In this case, primaryconfiguration information (e.g., line group size, number of consumers,etc.) is also apt to be static and will not change from line group toline group. Rather, the new configuration information that is providedto a line buffer interface unit mainly identifies the new line group(e.g., the location of the line group within memory, etc.). Morecomplicated potential arrangements/designs are possible, however. Someof these are described in more detail immediately below.

FIG. 9d depicts an embodiment of the contents of a line buffer interfaceunit's register space (e.g., the contents of register space 905_1 ofFIG. 9b ). A description of some of the register fields immediatelyfollows.

The LB_Enable field 921 essentially enables a line buffer interface unitand is “set” as part of the process of taking the line buffer interfaceunit from the free pool. The Num_Channels field 922 defines the numberof channels within the line group's image data. In an embodiment, theNum_Channels field 922 can be used to determine the total amount of dataper line group. For example, a video stream often includes a framesequence of red (R) pixels, a frame sequence of blue (B) pixels and aframe sequence of green (G) pixels. Thus, for any line group, there areactually three line groups worth of information (R, G and B).

The Num_Consumers field 923 describes the number of consumers that willrequest the line group. In an embodiment, the line buffer interface unitwill be entered to the free pool after a line group instance has beendelivered a number of times equal to the value in the Num_Consumersfield 923.

The Row_Width field 924 defines the width of a full line group (e.g., innumber of pixels). Note that the Row_Width 924 value can be expressed asan X coordinate value provided by the compiler. The FB_Rows field 926defines the height of a full line group (e.g., in number of pixels).Note that the FB_Rows field 924 can be expressed as a Y coordinate valueprovided by the compiler.

The FB_Base_Address field 930 defines the location of the line group inthe line buffer unit memory. In a first operational mode, referred to as“full” line group mode, a full sized line group is accessed in memory(line groups are received from producers and delivered to consumers ascontaining the full amount of their respective data). In the full linegroup mode, the Num_Channels field 922, the Row_Width field 924 and theFB_Rows field 926 can be used with the FB Address field 930 to determinethe range of addresses that are to be applied to memory to completelyaccess a full line group. Additionally, these same parameters can beused to “translate” a request from a sheet generator that has requestedthe line group in X, Y coordinates into a linear memory address.

The VB_Enable, VB_Rows, VB_Cols, Num_Reuse_Rows and VB_Base_Addressfields 925, 927, 928, 931 are used in another operational mode, referredto as the “virtually tall” line group mode, which is described in detailfurther below.

Whereas FIG. 9d displayed the configuration register space 905 for asingle line buffer interface unit, by contrast, FIG. 9e shows anembodiment of the contents of global configuration register space 907for the line buffer unit circuitry 901 as a whole. Whereas the per linebuffer interface unit register space of FIG. 9d is focused on a specificline group, by contrast, the global register space 907 of FIG. 9e isfocused on understanding the parsing of different line groups from asame image as well as other information that is specific to theproducer/consumer combination that are associated with the processing ofthe image.

As observed in FIG. 9e , an embodiment of the global register spaceincludes the number of channels 932 and the number of consumers 933 fora particular image. For simplicity, the register space of FIG. 9e onlycontemplates one image with one set of producers and consumers (e.g.,only a single video stream and a single point in a DAG). Conceivably,multiple instances of the register space of FIG. 9e could be allocatedto permit the line buffer unit circuitry to effectively multi-task.

A first form of multi-tasking is within a DAG or software pipeline thatis implemented on the image processor. Here, the same line buffer unitcould be configured to handle the line grouping for two different nodeswithin the DAG or for two different stages of the pipeline (that is, asingle line buffer unit could support more than one stencil processor).The different nodes/stages could easily have different numbers ofconsumers but in many cases are likely to have the same image andstencil size characteristics. A second form of multi-tasking is acrossmultiple different DAGs and/or multiple different pipelines that areimplemented on the same image processor hardware. For example, an imageprocessor having four stencil processors could concurrently execute twocompletely different two-stage pipelines that respectively processcompletely different image sizes with completely different stencildimensions.

Returning to the particular embodiment of FIG. 9e , note that anyparticular node in a DAG or between pipeline stages can be characterizedat a high level by the number of channels in the image, the image size,the dimensions of the applicable stencil and the number of consumers ofthe line groups (FIG. 9e again assumes one producer per line group butconceivably more than one producer could write to a single line group inwhich case the global register space of FIG. 9e would also include afield for the number of producers). The Num_Channels and Num_Consumersfields 932, 933 are essentially the same as the corresponding fields922, 923 of FIG. 9 c.

The Image_Size and Stencil_Dimension fields 934, 935 essentiallydescribe the dimensions of the image to be processed and the dimensionsof the stencil that will operate on the line groups that are to becarved from the image respectively. Note that both fields 934, 935 canbe expressed in terms of X, Y coordinate values and can be provided fromthe compiler. Additionally, in an embodiment, control logic circuitrywithin the line buffer circuitry unit (not shown in FIG. 9b ) uses theImage_Size and Stencil_Dimension fields 934, 935 to determine theRow_Width 924, FB_Rows 926 and FB_Base_Address values 930 that areloaded into a line buffer interface unit's register space when the linebuffer interface unit is assigned to handle line groups from theproducer/consumer set that the global information pertains to. In analternate or further embodiment, image size is expressed as two separatevalues, image_width and image_height, which may have their ownseparately addressable register space. Likewise, stencil size may beexpressed as two separate values, stencil_width and stencil_height,which may have their own separately addressable register space.

Row_Width 924 is directly obtainable from the Image_Size 934information. For example, if Image_Size is expressed as the X, Ycoordinate pair at the farthest pixel from the image origin (the upperright hand corner if the origin is at the lower left hand corner),Row_Width can be determined as the X coordinate value.

The FB_Rows and FB_Base_Address fields 926, 930 can be determined fromthe Image_Size and Stencil_Dimension fields 934, 935. Here,specifically, the height of each line group (FB_Rows 926) can becalculated from the height of the image (Y coordinate value ofImage_Size 934) and the stencil height (Y coordinate value ofStencil_Dimension 935). Once the height of the line groups is known, thenumber of line groups that are to be parsed from the image and thestarting linear address for each such line group in memory(FB_Base_Address 930) can also be determined.

Thus, in an embodiment, when a line buffer unit is assigned to handle aline group for a particular producer/consumer combination whose globalregister space is characterized by the register fields of FIG. 9e , theabove described determinations are calculated on the fly and each ofFB_Width 924, FB_Rows 926, Base_Address 934 are loaded into the linebuffer interface unit's specific register space along with Num_Channels922 and Num_Consumers 923 which copy over directly. Logic circuitry anddata paths may therefore exist between the global register space andeach instance of line buffer interface unit register space to performthese determinations and data transfers.

In an alternate embodiment, the compiler performs each of thesecalculations thereby eliminating much if not all of the global registerspace altogether. Here, for instance, the compiler can determine theBase_Address value for each line group and load the values in a look-uptable within the line buffer circuitry unit. The values are called fromthe look-up table and loaded into a line buffer interface unit'sregister space as their corresponding line groups are configured for.Different combinations between these two extremes (hardware on-the-flyvs. static compiler determined) may also be implemented.

Although embodiments above emphasized the keeping of configurationinformation in register circuitry (“register space”), in other orcombined embodiments, configuration information may be kept in memory(such as buffer unit memory) or other memory or information keepingcircuitry.

c. Line Buffer Unit Embodiments & Full Line Group Mode Vs. VirtuallyTall Mode

The discussions above have largely been directed to “full line group”mode in which line groups are referred to and passed between the sheetgenerators and line buffer unit as complete, entire line groups. Inanother mode, referred to as “virtually tall”, line groups are referredto and passed between the sheet generators as a full width upper portionand a lower portion that is completed in separate, discrete segments.

FIGS. 10a and 10b show a depiction of an exemplary virtually tall modesequence. As observed in FIG. 10a , a line group is initially formed asan upper portion 1003 of full width rows and a first lower portion1004_1 having only a first, shorter segment of width. The initialformation of a line group may be provided to a line buffer unit by aproducing sheet generator, or, may be provided by a line buffer unit toa consuming sheet generator.

In the case of a producer, the line group is formed after the stencils1002 have processed over the lower portion 1004_1 (the approximatestencil positioning is observed in FIG. 10b ). After the producerstencil processor has processed over the lower portion 1004_1 thestencils continue forward horizontally to the right. Eventually theywill process over a next lower portion 1004_2. Upon completion of thenext lower portion 1004_2, the next lower portion 1004_2 is sent fromthe sheet generator to the line buffer unit which stores it in memory inthe correct location, e.g., “next to” first lower portion 1004_1. Theprocess continues until the line group is fully written into line bufferunit memory.

In the case of consumers, the line group is initially delivered to thesheet generator as observed in FIG. 10a . The stencil processor operatesover the first portion 1004_1 of the line group. Upon nearing thecompletion of the processing of the first portion 1004_1 the sheetgenerator will request the next lower portion 1004_2 which is fetchedfrom memory and delivered by the line buffer unit. The process continuesuntil the line group is completely processed.

Note that for both producers and consumers, lower portions arespecifically identified by the sheet generator. That is, in both theproducer case and the consumer case, lower portion 1004_2 isspecifically identified by the sheet generator and the line buffer unitspecifically accesses memory to store/fetch lower portion 1004_2. In anembodiment, the sheet generator identifies lower portion 1004_2 throughX, Y coordinate values that are contemplated based on informationprovided by the compiler (for example, any corner of lower portion1004_2, all four corners of lower portion 1004_2, just an X coordinatevalue, etc.).

FIG. 11a shows a first (more simplistic) embodiment of the circuitrywithin a line buffer interface unit 1104. As observed in FIG. 11a , theline buffer interface unit includes address translation circuitry 1106to convert the identity of a line group or portion thereof (such aslower portion 1004_2 of FIG. 10b ) that is identified by one or more X,Y coordinate values into a linear address for accessing line buffer unitmemory. That is, line groups can be deemed to be “mapped” into linebuffer unit memory. The translation circuitry 1106 essentiallycomprehends this mapping in X,Y terms and can convert the same tospecific linear memory addresses.

The ability to comprehend the mapping is based on information withinconfiguration register space 1105, an embodiment of which was providedabove in FIG. 9d . Here, with knowledge of Row_Width 924, FB_Rows 926and FB_Base_Address 931 the translation unit can “comprehend” the sizeand location of the full line group in memory. As such, for example, inthe virtually tall mode, a request for a lower portion based on any Xcoordinate value (e.g., if the lower portion is referenced relative tothe line group) or X,Y coordinate location (e.g., if the lower portionis referenced relative to the image frame) is sufficient to identifywhat portion is being referred to by the sheet generator. Additionally,Vb_Rows 927 and Vb_Cols 928 essentially define the dimensions of thelower portions. With knowledge of the dimensions of the upper and lowerportions the amount of data to be accessed to/from buffer memory is alsoreadily determinable. These same concepts may also to apply to fullwidth line groups. For example, any full width line group may beidentified by its X,Y location within an image. Additionally, in someembodiments, a full width line group may be passed through the networkvia a sequence of atomic requests/responses that reference smallerchunks of a full width line group by way of X and/or Y coordinatevalues.

The translation circuitry 1106 could also be used in an abstractaddressing mode in which the Base_Address_Field 931 is not populated andthe sheet generators refer to line groups as X,Y coordinates within animage frame. In this case, if the translation circuitry 1006 is coupledto or otherwise apprised of some of the information in the globalregister space of FIG. 9e (e.g., Image_Size, Stencil_Size), thetranslation circuitry 1106 could calculate all pertinent information forthe line group (its dimensions and location within the frame) andconvert the same to linear addresses used for accessing line buffer unitmemory. In another embodiment, the translation circuitry 1106 determinesthe Base_Address_Field value 931 outright (based on global typeinformation and one or more X, Y coordinates describing the line group)and loads it into its own register space 1105.

The line buffer interface unit embodiment of FIG. 11a also supports alinear addressing mode in which X,Y coordinate values are not used torefer to a line group (rather, traditional linear addresses are used).For the linear addressing mode, bypass paths 1140 circumvent the addresstranslation circuitry 1106. In an embodiment, regardless of whichaddressing mode is used at the line buffer interface unit input, theline buffer interface unit provides standard linear memory addresses foraddressing line buffer unit memory. Referring briefly back to FIG. 9b ,the linear addresses are provided to an arbiter. Memory interface 908resolves colliding memory access requests and accesses line buffer unitmemory 902.

As discussed at length above, a sheet generator may refer to a linegroup with one or more X, Y coordinate values. In another embodiment,rather than the sheet generators identifying a next line group in fullline group mode or a next lower portion in virtually tall mode, thesheet generators simply issue a request akin to “next” (e.g., therequest only indicates a “next” full line group or “next” lower portionor “next” image data within the same full/virtually tall line group isbeing referred to without any coordinates).

To support this avenue of communication, the line buffer unit and/orline buffer unit interface includes state register space to comprehendwhat the next line group/portion is. FIG. 11b shows an enhancedembodiment of a line buffer interface unit that keeps pointer stateinformation so that the sheet generators can simply refer to a “next”lower portion of a line group in virtually tall mode rather than havingto specify its location with X,Y coordinates. Here, a write pointer 1141is maintained by pointer control logic circuitry 1143 that keeps trackof the lower portions that have been provided by the producing sheetgenerator. Essentially the write pointer 1141 stores the location of the“next” portion that the producer is scheduled to deliver. In addition,the pointer state information permits sheet generators to refer only toa “next” full width line group (in full width mode) without having tospecify any X,Y coordinates (because the line buffer interface unit candetermine where the next full width line group for the image is).

In an embodiment, the pointer is articulated as one or more X, Ycoordinates and the translation circuitry converts the same into alinear address. When the next portion is received, the pointer 1141 isupdated by pointer control logic circuitry 1143 to point to the portionthat will follow the portion that has just been received. Read pointers1142 operate similarly but a separate read pointer is kept for eachconsumer (again, only one producer is assumed for convenience).

In the case of full line group mode, the location of the “next” fullwidth line group is determinable from the global register informationand a similar arrangement of pointers that are kept at a global level.

d. Implementation Embodiments

It is pertinent to point out that the various image processorarchitecture features described above are not necessarily limited toimage processing in the traditional sense and therefore may be appliedto other applications that may (or may not) cause the image processor tobe re-characterized. For example, if any of the various image processorarchitecture features described above were to be used in the creationand/or generation and/or rendering of animation as opposed to theprocessing of actual camera images, the image processor may becharacterized as a graphics processing unit. Additionally, the imageprocessor architectural features described above may be applied to othertechnical applications such as video processing, vision processing,image recognition and/or machine learning. Applied in this manner, theimage processor may be integrated with (e.g., as a co-processor to) amore general purpose processor (e.g., that is or is part of a CPU ofcomputing system), or, may be a stand alone processor within a computingsystem.

The hardware design embodiments discussed above may be embodied within asemiconductor chip and/or as a description of a circuit design foreventual targeting toward a semiconductor manufacturing process. In thecase of the latter, such circuit descriptions may take the form ofhigher/behavioral level circuit descriptions (e.g., a VHDL description)or lower level circuit description (e.g., a register transfer level(RTL) description, transistor level description or mask description) orvarious combinations thereof. Circuit descriptions are typicallyembodied on a computer readable storage medium (such as a CD-ROM orother type of storage technology).

From the preceding sections is pertinent to recognize that an imageprocessor as described above may be embodied in hardware on a computersystem (e.g., as part of a handheld device's System on Chip (SOC) thatprocesses data from the handheld device's camera). In cases where theimage processor is embodied as a hardware circuit, note that the imagedata that is processed by the image processor may be received directlyfrom a camera. Here, the image processor may be part of a discretecamera, or, part of a computing system having an integrated camera. Inthe case of the later the image data may be received directly from thecamera or from the computing system's system memory (e.g., the camerasends its image data to system memory rather than the image processor).Note also that many of the features described in the preceding sectionsmay be applicable to a graphics processor unit (which rendersanimation).

FIG. 12 provides an exemplary depiction of a computing system. Many ofthe components of the computing system described below are applicable toa computing system having an integrated camera and associated imageprocessor (e.g., a handheld device such as a smartphone or tabletcomputer). Those of ordinary skill will be able to easily delineatebetween the two.

As observed in FIG. 12, the basic computing system may include a centralprocessing unit 1201 (which may include, e.g., a plurality of generalpurpose processing cores 1215_1 through 1215_N and a main memorycontroller 1217 disposed on a multi-core processor or applicationsprocessor), system memory 1202, a display 1203 (e.g., touchscreen,flat-panel), a local wired point-to-point link (e.g., USB) interface1204, various network I/O functions 1205 (such as an Ethernet interfaceand/or cellular modem subsystem), a wireless local area network (e.g.,WiFi) interface 1206, a wireless point-to-point link (e.g., Bluetooth)interface 1207 and a Global Positioning System interface 1208, varioussensors 1209_1 through 1209_N, one or more cameras 1210, a battery 1211,a power management control unit 1212, a speaker and microphone 1213 andan audio coder/decoder 1214.

An applications processor or multi-core processor 1250 may include oneor more general purpose processing cores 1215 within its CPU 1201, oneor more graphical processing units 1216, a memory management function1217 (e.g., a memory controller), an I/O control function 1218 and animage processing unit 1219. The general purpose processing cores 1215typically execute the operating system and application software of thecomputing system. The graphics processing units 1216 typically executegraphics intensive functions to, e.g., generate graphics informationthat is presented on the display 1203. The memory control function 1217interfaces with the system memory 1202 to write/read data to/from systemmemory 1202. The power management control unit 1212 generally controlsthe power consumption of the system 1200.

The image processing unit 1219 may be implemented according to any ofthe image processing unit embodiments described at length above in thepreceding sections. Alternatively or in combination, the IPU 1219 may becoupled to either or both of the GPU 1216 and CPU 1201 as a co-processorthereof. Additionally, in various embodiments, the GPU 1216 may beimplemented with any of the image processor features described at lengthabove.

Each of the touchscreen display 1203, the communication interfaces1204-1207, the GPS interface 1208, the sensors 1209, the camera 1210,and the speaker/microphone codec 1213, 1214 all can be viewed as variousforms of I/O (input and/or output) relative to the overall computingsystem including, where appropriate, an integrated peripheral device aswell (e.g., the one or more cameras 1210). Depending on implementation,various ones of these I/O components may be integrated on theapplications processor/multi-core processor 1250 or may be located offthe die or outside the package of the applications processor/multi-coreprocessor 1250.

In an embodiment one or more cameras 1210 includes a depth cameracapable of measuring depth between the camera and an object in its fieldof view. Application software, operating system software, device driversoftware and/or firmware executing on a general purpose CPU core (orother functional block having an instruction execution pipeline toexecute program code) of an applications processor or other processormay perform any of the functions described above.

Embodiments of the invention may include various processes as set forthabove. The processes may be embodied in machine-executable instructions.The instructions can be used to cause a general-purpose orspecial-purpose processor to perform certain processes. Alternatively,these processes may be performed by specific hardware components thatcontain hardwired logic for performing the processes, or by anycombination of programmed computer components and custom hardwarecomponents.

Elements of the present invention may also be provided as amachine-readable medium for storing the machine-executable instructions.The machine-readable medium may include, but is not limited to, floppydiskettes, optical disks, CD-ROMs, and magneto-optical disks, FLASHmemory, ROMs, RAMs, EPROMs, EEPROMs, magnetic or optical cards,propagation media or other type of media/machine-readable mediumsuitable for storing electronic instructions. For example, the presentinvention may be downloaded as a computer program which may betransferred from a remote computer (e.g., a server) to a requestingcomputer (e.g., a client) by way of data signals embodied in a carrierwave or other propagation medium via a communication link (e.g., a modemor network connection).

In the foregoing specification, the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modifications and changes may be made theretowithout departing from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than a restrictivesense.

1. (canceled)
 2. A device configured to manage a pool of line groupbuffers for multiple different stencil processors, the devicecomprising: a plurality of stencil processors; a memory deviceconfigured to store line group data for the pool of line group buffers;and a plurality of line buffer interface units, each line bufferinterface unit being configurable to manage read and write requests fora respective line group buffer of the pool of line group buffers storedby the memory device, each line group buffer being a respectivepartition of storage within the memory device, wherein the device isconfigured to reassign line buffer interface units to manage respectiveline group buffers for different stencil processors of the device. 3.The device of claim 2, wherein the device is configured to manage thepool of line group buffers for multiple different stencil processorsexecuting different stages of a same image processing pipeline.
 4. Thedevice of claim 2, wherein the device is configured to manage the poolof line group buffers for multiple different stencil processorsexecuting different image processing pipelines.
 5. The device of claim2, wherein the line buffer interface unit is selected from a line bufferinterface units pool within a line buffer unit circuitry, wherein theselected line buffer interface unit is configured with configurationinformation including position information or a linear memory address ofone of a plurality of line groups, wherein the selected line bufferinterface unit is configured to store the one of the plurality of linegroups in the memory device and provide the one of the plurality of linegroups from the memory device, and wherein each of the plurality of linebuffer interface units is assigned a new line group of the plurality ofline groups after proceeding the one of the plurality of line groups. 6.The device of claim 5, wherein the line buffer interface unit of theline buffer interface units pool is configured to receive a writerequest from one or more producer processor of the multiple stencilprocessors, to identify, within a line group buffer assigned to the linebuffer interface unit and stored by the memory device, a write locationcorresponding to the write request, and to store data at the writelocation within the line group buffer assigned to the line bufferinterface unit.
 7. The device of claim 6, wherein the line bufferinterface unit of the line buffer interface units pool is configured toreceive a read request from one or more consumer processors of themultiple stencil processors, to identify, within the line group bufferassigned to the line buffer interface unit and stored by the memorydevice, a read location corresponding to the read request, and toprovide data stored at the read location within the line group bufferassigned to the line buffer interface unit.
 8. The device of claim 7,wherein, based on that a last producer processor has written to theplurality of the line groups and a last consumer processor has beenprovided with data stored at corresponding line group, the line bufferinterface unit is returned to the line buffer interface units pool andconfigured to proceed a next line group of the plurality of line groups.9. The device of claim 6, wherein the configuration informationcomprises configuration parameters that specify respective sizes of linegroup buffers managed by the line buffer interface units and that arebased on output sizes of respective kernel programs that provide writerequests to the line buffer interface units.
 10. The device of claim 9,wherein the configuration parameters are stored in a respectiveprogrammable configuration space of each respective line bufferinterface unit.
 11. The device of claim 5, wherein the device isconfigured to reassign the line buffer interface unit to manage adifferent line group buffer stored by the memory device.
 12. A methodfor managing a pool of line group buffers for multiple different stencilprocessors, the method being performed by a device comprising aplurality of stencil processors, a memory device configured to storeline group data for the pool of line group buffers, and a plurality ofline buffer interface units, the method comprising: reassigning linebuffer interface units to manage respective line group buffers fordifferent stencil processors of the device; and managing, by each linebuffer interface unit, read and write requests for a respective linegroup buffer of the pool of line group buffers stored by the memorydevice, each line group buffer being a respective partition of storagewithin the memory device.
 13. The method of claim 12, further comprisingmanaging the pool of line group buffers for multiple different stencilprocessors executing different stages of a same image processingpipeline.
 14. The method of claim 12, further comprising managing thepool of line group buffers for multiple different stencil processorsexecuting different image processing pipelines.
 15. The method of claim12, wherein configuration parameters that specify the respective sizesof line group buffers managed by the line buffer interface units arebased on output sizes of respective kernel programs that provide writerequests to the line buffer interface units.
 16. The method of claim 15,further comprising storing the configuration parameters that specify therespective sizes of lien group buffers managed by the line bufferinterface units in a respective programmable configuration space of eachrespective line buffer interface unit.
 17. The method of claim 12,further comprising: receiving, by a line buffer interface unit, a writerequest from a producer processor; identifying, by the line bufferinterface unit within a line group buffer assigned to the line bufferinterface unit and stored by the memory device, a write locationcorresponding to the write request; and storing data at the writelocation within the line group buffer assigned to the line bufferinterface unit.
 18. The method of claim 17, further comprising:receiving, by the line buffer interface unit, a read request from one ormore consumer processors; identifying, by the line buffer interface unitwithin the line group buffer assigned to the line buffer interface unitand stored by the memory device, a read location corresponding to theread request; and providing data stored at the read location within theline group buffer assigned to the line buffer interface unit.
 19. Themethod of claim 12, further comprising: converting, by translationcircuitry of a line buffer interface unit, a read or write request intoa linear address within a line group buffer managed by the line bufferinterface unit and stored by the memory device.
 20. The method of claim12, further comprising reassigning a line buffer interface unit tomanage a different line group buffer stored by the memory device. 21.The method of claim 20, further comprising reassigning the line bufferinterface unit upon the line buffer interface unit handling alloutstanding read requests for a previously assigned line group bufferstored by the memory device.